1. Field of the Invention
This invention pertains to a method of and apparatus for making and dispensing carbonated water with a double diaphragm continuous delivery pneumatically powered water pump, wherein gas pressure in excess of a reduced water supply pressure, is kept upon the diaphragms preventing diaphragm inversion.
This invention also pertains to a method of and apparatus for boosting water pressure with a double diaphragm pneumatic pump wherein a propellent exhaust gas back pressure on the diaphragms is kept higher than a water supply pressure for preventing diaphragm inversion.
2. Description of the Prior Art
The most relevant prior art is documented in J. R. McMillin et al U.S. Pat. No. 4,304,736 of Dec. 8, 1981. This patent documents a complete soft drink beverage dispensing system of the post-mix type having pneumatic syrup pumps and a double piston continuous delivery pneumatic water pump for delivering either tap or un-pressurized water to a carbonator vessel. The double piston pump in this dispenser is the specific subject matter of J. R. McMillin et al U.S. Pat. No. 4,354,806 and this pump has a control valve which is the specific subject matter of G. A. Tracy U.S. Pat. No. 4,310,025. Reference may be had to these patents for an extensive history of the prior art leading up to the development of the pneumatically powerable dispensing system of U.S. Pat. No. 4,304,736. This dispenser and its componentry have been tremendously successful and represent the world's first extensively successful soft drink dispenser using syrup in bag-in-box (BIB) packaging. This dispenser is in extensive use in the U.S., Australia, Spain, Italy and elsewhere, and it produces and dispenses a high quality soft drink beverage.
The problems that have developed with the dispenser according to U.S. Pat. No. 4,304,736 have to do with relatively high cost, complexity, gas usage, large size, and maintenance. These problems manifest themselves primarily in the double piston water pump. The double piston pump requires pistons, piston rings, shaft seals, stainless steel cylinders, discrete inboard and outboard cylinder heads, and quite large tie rods to hold it together. It is quite complex and has a great many precision and expensive parts. An extra quantity of propellent gas is consumed to overcome the frictional losses incurred by the piston rings. The pump is quite large with all its discrete parts and large tie rods, and it takes up a lot of room inside of the dispenser. The double piston pump requires a fair amount of relatively sophisticated maintenance with periodic replacement of piston rings and seals, tightening and/or replacement of the many propellent gas lines, and lubrication. The wrong type of lubrication will effectively contaminate the water and cause decarbonation and foaming upon dispensing. If the piston rings leak, blown by water is also exhausted by the control valve and the valve may tend to freeze up as the propellent gas pressure drops and the water leakage is exhausted.
Much interest has been focused upon the development of a double diaphragm continuous delivery syrup pump to replace the single action diaphragm syrup pump in the dispenser of U.S. Pat. No. 4,304,736. A specific example of a commercially successful double diaphragm syrup pump is documented in W. S. Credle, U.S. Pat. No. 4,436,493 of Mar. 13, 1984. The reader is referred to the extensive cited reference list of U.S. Pat. No. 4,436,493 for further examples of prior pumps and componentry. Functionally similar double diaphragm pumps are available under the names McCann, Bellofram, Flojet, Shurflow, Wilden, Rupp, ITT and others. Another pump of this type is in W. R. Scholle U.S. Pat. No. 4,123,204. The pump of Credle U.S. Pat. No. 4,436,493 has a cost which is about 1/2 of the cost of the pump of McMillin et al U.S. Pat. No. 4,354,806. Serious efforts have been made to try and make the Credle pump work in the dispenser of U.S. Pat. No. 4,304,736 but all efforts to date have failed.
The reason for the failures is that the diaphragms fail and wear and burst from inversion of the diaphragms due to the unpredictable pressure of the water supply. The double piston water pump will draw water under partial vacuum, or positively take and displace pressurized water. It makes no difference whether the water supply is pressurized or not because the piston rings seal both ways, specifically under pressure or vacuum and to either side of the rings. The double diaphragm pump has never been able to do this and it must be constructed to pull under vacuum only. In a double cylinder pump, one side is being pressurized while the other side is exhausting. The pump diaphragms are normally biased toward the liquid side by the pressure on the gas side or by the partial vacuum on the liquid side. During the exhaust cycle, this propellent pressure is removed from the diaphragm and the diaphragm is biased by this partial vacuum on the liquid side. In the power or pumping cycle, the diaphragm is biased into the liquid by the propellent pressure.
However, if an automatic pressurized source of water such as a municipal water line or an automatic well system is connected to the pump, upon the start of the exhaust and refill cycle the diaphragm is forced into the gas chamber by the water pressure and inversion of the diaphragm takes place. When the pumping cycle again starts, the diaphragm is blown back into the syrup chamber by the propellent pressure and reversion of the diaphragm takes place. In the drawings, on FIG. 2, side R shows the normal configuration of the diaphragm during propellent pressurization and pumping, and side I shows inversion of the diaphragm due to source water pressure.
Needless to say, continued inversion, reversion, inversion, reversion and so on of the diaphragm leads to its early and premature failure. All sorts of bizarre events occur upon perforation of the diaphragm. Water is free to get into the gas system, and gas, such as CO.sub.2, can be fed into the water lines and start copper sulfate production. The beverage dispenser is also put out of order.
It is necessary to boost water pressure in order to carbonate the water. An ambient temperature carbonator requires about 100 PSIG water pressure and a cold carbonator requires about 30 PSIG water pressure for attaining the industry standard of 4.5 volumes of carbonation.
The existing booster systems are primarily electric and utilize a motor driven pump of some type. The most extensively commercialized water booster vane pump is a carbon sliding pump made by Procon and powered by an electric motor under the control of a relay. These are expensive, but are accepted and extensively used. Electric vibrator water pumps are used in very low volume dispensers. Some dispensers have dropped the gas pressure in the carbonator to let water in. Booth, Inc. has made most of these examples. The only successful pneumatic water pressure booster has been the double piston pump of J. R. McMillin et al U.S. Pat. No. 4,304,736. No party has been successful in boosting water pressure with a diaphragm pump. A low cost highly reliable and simple pneumatic water pressure booster would be very usable in ice cooled beverage equipment, at special events where electricity is not available and for many other presently unrecognized uses.